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BOUNDARY LAYER SEPARATION CONTROL USING A STEP-WALL CONICAL DIFFUSER WITH AN ANNULAR INLET

Kin Pong Lo
Department of Mechanical Engineering Stanford University 488 Escondido Mall, Building 500 Room 501W, Stanford, CA 94305

Christopher J. Elkins
Department of Mechanical Engineering Stanford University 488 Escondido Mall Stanford, California 94305

John K. Eaton
Dept. of Mechanical Engineering Stanford University 488 Panama Mall Stanford, CA 94305 USA

Abstract

Practical applications of conical diffusers often involve an upstream annular flow passage created by a center body that is present for structural or other design requirements. The wake of the center body can cause the diffuser wall boundary layer to separate in an unpredictable manner. Flow separation can degrade the diffuser performance and fatigue downstream components and therefore must be controlled. A step-wall diffuser can be used to control the wall separation by fixing its location. The present experiment utilizes magnetic resonance velocimetry to acquire three-component mean velocity measurements for a set of step-wall conical diffusers with an annular inlet. The results show that the step separation bubble is predictable and stable. Reduction in the overall diffuser length is achieved by using three-dimensional perturbations to shorten the reattachment length of the step separation bubble.